Action Points

No statistically significant link was found between infant exposure to antibiotics and subsequent weight gain through age 7 years.

Note that the study suggests that although there are many reasons to limit antibiotic exposure in young, healthy children, weight gain may not be one of them.

No statistically significant link was found between infant exposure to antibiotics and subsequent weight gain through age 7 years, a large retrospective study showed.

Infants who were exposed to antibiotics during the first 6 months of life did not see a significant increase in the rate of change in weight, with an estimated increase of 0.05 kg (less than 1 lbs) from 2 to 5 years of age (0.7% rate of change, P=0.07), reported Jeffrey S. Gerber, MD, PhD, of The Children's Hospital of Philadelphia, and colleagues.

Subanalyses by antibiotic type (narrow spectrum, broad spectrum, or macrolide) also found a nonsignificant difference between infant antibiotic exposure and rate of change in weight (P=0.51), they wrote in the Journal of the American Medical Association.

Joseph Skelton, MD, of Wake Forest Baptist Medical Center in Winston-Salem, N.C., characterized the study as "well-conducted." He that there has been lots of interest in antibiotic exposure and development of obesity, with a few smaller studies in humans and rich data in animal models showing that early antibiotic use may contribute to later obesity.

"While association does not prove (or disprove) causation, the size of this study does give the best evidence to date of a lack of association of antibiotic exposure to development of childhood obesity," Skelton, who was not involved with the research, wrote in an email to MedPage Today. "The number of patients included in this study can reassure a parent, for now, that the choice to treat an infection with an antibiotic is unlikely to put their child at risk for obesity, though much research still needs to be done."

The retrospective longitudinal cohort study examined data from 38,522 singleton children, 5,287 (14%) of whom were exposed to antibiotics at a mean age of 4.3 months. Of these, 24% received broad spectrum antibiotics, while 5% received macrolides.

The children were born between Nov. 1, 2001, and Dec. 31, 2011, at 35 weeks' gestational age or older, and with birth weight of ≥2000 g and in the fifth percentile or higher for gestational age. Participants had to undergo a preventive health visit within 14 days of life and at least two additional visits in the first year of life.

The authors reported that 79% of participants received only one course. By 24 months of age, 67% of children had received any antibiotics, with broad-spectrum comprising 52% of all prescriptions and macrolides consisting of 19% of antibiotics received.

Secondary analyses examining antibiotic exposure within the first 24 months of life did find a statistically significant association in the increase in rate of change in weight (2.1%, P=0.001), with an estimated 0.15 kg gain from age 2 to 5 years. Subanalysis also revealed significant differences by number of antibiotic courses, ranging from a 1.8% weight difference for one course of antibiotics (P=0.01) to a 2.4% for three or more courses (P=0.002).

However, Gerber's team argued that this is not "a clinically meaningful association" between early life antibiotic use and childhood weight gain, and it is merely reflecting "the robust statistical power afforded by the sample size" of their study. They also suggest that their analysis differs from prior studies on exposure to antibiotic use in children and weight gain specifically because of the exposure time.

"The primary exposure ... was chosen based on the biological mechanism through which antibiotics increase adiposityin experimental animals: pertubations in the developing gut microbiome," wrote Gerber and colleagues. "The lack of an association in subanalyses of children exposed to repeated antibiotic courses and those given agents that would target a broader range of gut microbiota supports our conclusions."

Another difference between this and prior studies was the decision to measure weight trajectory instead of body mass index (BMI), because BMI is a ratio measure, and thus may include potential for bias.

Among a small group of twins (46 pairs, 92 children), there was also no significant association in weight gain in a twin exposed to antibiotics in the first 6 months compared with the unexposed twin (P=0.30).

Study limitations included the fact that adiposity was not assessed, so antibiotic exposure could be associated with changes in adiposity without impacting weight or BMI. There was also the potential for misclassification for antibiotics that were not taken or taken, but not documented, and the results may not be generalizable to children outside the U.S. healthcare setting.

"The study also doesn't answer other questions, such as what kind of antibiotics may or may not put someone at risk for later obesity," Skelton noted.

Gerber and co-authors disclosed no relevant relationships with industry.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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